2022 AMC 8 Problems/Problem 20
The grid below is to be filled with integers in such a way that the sum of the numbers in each row and the sum of the numbers in each column are the same. Four numbers are missing. The number in the lower left corner is larger than the other three missing numbers. What is the smallest possible value of ?
The sum of the numbers in each row is . Consider the second row. In order for the sum of the numbers in this row to equal , the two shaded numbers must add up to : If two numbers add up to , one of them must be at least : If both shaded numbers are no more than , their sum can be at most . Therefore, for to be larger than the three missing numbers, must be at least . We can construct a working scenario where : So, our answer is .
The sum of the numbers in each row is and the sum of the numbers in each column is
Let be the number in the lower middle. It follows that or
We express the other two missing numbers in terms of and as shown below: We have and Note that the first inequality is true for all values of We only need to solve the second inequality so that the third inequality is true for all values of By substitution, we get from which
Therefore, the smallest possible value of is
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